The moc1 gene in Schizosaccharomyces pombe was found as to overcome sterility caused by high expression of adenylyl cyclase. The moc1 gene was found to be identical with sds23 and psp1. Although psp1 has been reported to be essential for growth, sds23 has not been. To clarify this apparent discrepancy, we first assessed independently the phenotypes of the moc1 disruptant. We confirmed that the deletion mutant of moc1 is sterile, sensitive to high salt, and grows slowly at higher and lower temperatures, and that mutant cells are elongated. Besides these phenotypes, we found that viability of the moc1 disruptant was rapidly lost at the stationary phase. We confirmed that the Moc1 protein is phosphorylated in the stationary phase and also under nitrogen-starved conditions. We examined the significance of this phosphorylation of Moc1 by creating the S333A or S333D mutant Moc1. Interestingly, while S333D mutant Moc1 is lower in inducing sexual development, S333A mutant Moc1 is higher in this than the wild type, suggesting that phosphorylation of Moc1 affects sexual development. The other phenotypes, such as sensitivity to high salt and higher temperature and elongation of cells, were not affected by mutation of S333A nor S333D. We found that Moc1-GFP localized to both the cytosol and the nucleus during mitotic growth, but accumulated in the nucleus in mating cells and then enriched in spores, and that this localization shift was negatively regulated by the cAMP pathway. This and the observations above suggest that nuclear localized Moc1 is an inducer of sexual development. Thus, in addition to the roles of moc1/sds23/psp1 in mitosis and stress response, it is also important for the survival and sexual development of fission yeast, but phosphorylation of Moc1 only affects the sexual development.